Telecom and Vodafone may be allowed to submit Trade Me-style "autobids" for the last block of "digital dividend" radio spectrum, a source close to the auction suggests.

It is understood a rule change is being considered because the auction currently under way has dragged on longer than officials expected.

The Ministry of Business, Innovation and Employment, which is running the auction, declined to comment.

Telecom and Vodafone are understood to have bid about $77 million for the spectrum block, the last of nine such blocks freed by the closure of analogue television, in an auction that started in November.

The reserve was set at $22m and the price had been rising by $3m a day. The auction was set to resume next week, according to the source.

It is understood that the ministry is now considering allowing the two companies to specify their maximum price through an autobid, which could potentially bring the auction to a close in just one day.

The Commerce Commission has yet to decide whether either telco should be allowed to buy the spectrum.

It is due to make a ruling by February 14.

The source speculated the commission would need a good reason to decline the purchase, given the high price the spectrum had already fetched and the boost it would provide to the Government's coffers.